The time-honored method for plating tin-lead alloys, commonly called Solder Plate, is to have these two metals present in solution as fluoborates with an excess of fluoboric acid and boric acid. In order to obtain smoother deposits, it is common to add various types of proteins, such as peptones, glue, gelatin or meat proteins. The fluoborate based bath containing peptone is most commonly used and it is commercialy successful in obtaining smooth matte deposits. Brighter tin-lead solder deposits can be obtained from these fluoborate based baths by adding various brightening agents, such as aromatic alkane pyridine compounds, ethylene oxide wetting agents and formaldehyde.
The main problem with these fluoborate based baths is the fluoborate ion itself. Fluoborates are not only highly poisonous but are also highly corrosive to the equipment used in the plating environment. Fluoborates are also difficult to remove from the waste water that follows the plating operation and presents a serious problem for the waste-disposal engineer.
U.S. Pat. No. 2,525,942 to Proell, patented Oct. 17, 1950 broadly discloses the use of concentrated solutions of various metals including lead in alkane sulfonic acids containing 1 to 5 carbon atoms in the alkyl group. The invention requires at least 10 percent by weight of the metal alkanesulfonate. The most advantageous pH of the electrolytic solution varies with the metal used and the pH designated for the lead electrolyte is between 4 and 5.
The article entitled "Electrodeposition Of Bright Tin-Lead Alloys From Alkanolsulfonate Bath," by N. Dohi and K. Obata, Proceedings of Interfinish 80, discloses the electrodeposition of tin-lead alloys using alkanolsulfonate baths. The alkanolsulfonates found to be suitable for the electrodeposition of tin-lead alloys were those having a short carbon chain and in which the hydroxyl group is on a carbon atom near the sulfonic acid group.